Do you see any console messages when you press those keys?
–
arrangeMar 19 '11 at 23:51

Yes, that's what I was saying, they appear to work correctly: after each key press (beginning with SysRq+E) I'm seeing status updates from the OS: that it synced the file systems and things like that. Even the last keypress SysRq+B appears to work (it says "... resetting") except for the fact that my laptop does not actually restart (as if the hardware does not receive the command required to reboot).
–
user12681Mar 20 '11 at 0:13

2

Maybe you have ACPI issues. Try booting with nolapic and acpi=off and acpi=bios
–
Janus TroelsenApr 21 '12 at 13:45

No, SysRq handlers will sometimes shut off at the unmount, and a hard reset is safe.
–
hexafractionAug 10 '12 at 15:31

1

Does SysRq+O (for Off) work? I used to have a system where that worked, but not reBoot, despite all my efforts.
–
taneliAug 17 '12 at 8:24

1 Answer
1

R - takes keyboard and mouse control from the X server. This can be useful if the X-Server crashed, you can change to a console and kill the X-Server or check the error log.
NOTE:- The documentation refers to this key's task as "Turns off keyboard raw mode and sets it to XLATE", but I suppose it's safe enough to assume that it takes back control from X.

E - sends SIGTERM to all processes except init. This means that an attempt is done to end the current processes except init, safely, e.g. saving a document.

I - sends SIGKILL to all processes except init. This means that all the processes except for init are killed, any data in processes that are killed will be lost.

S - writes all data from the disc cache to the hard-discs, it is a sync and is necessary to reduce the chances of data corruption.

U - remounts all mounted filesystems read-only. After using this key, you can reboot the system with Alt+SysRq+B without harming the system.

B - restarts the system without making steps to ensure that the conditions are good for a safe reboot, using this key alone is like doing a cold reboot.

Try without pressing R at begining of your sequence
or just do it in another seq.. give a litle time between those keystrokes and do this..